27 research outputs found
Ecosystem size-induced environmental fluctuations affect the temporal dynamics of community assembly mechanisms
Understanding processes that determine community membership and abundance is important for many fields from theoretical community ecology to conservation. However, spatial community studies are often conducted only at a single timepoint despite the known influence of temporal variability on community assembly processes. Here we used a spatiotemporal study to determine how environmental fluctuation differences induced by mesocosm volumes (larger volumes were more stable) influence assembly processes of aquatic bacterial metacommunities along a press disturbance gradient. By combining path analysis and network approaches, we found mesocosm size categories had distinct relative influences of assembly process and environmental factors that determined spatiotemporal bacterial community composition, including dispersal and species sorting by conductivity. These processes depended on, but were not affected proportionately by, mesocosm size. Low fluctuation, large mesocosms primarily developed through the interplay of species sorting that became more important over time and transient priority effects as evidenced by more time-delayed associations. High fluctuation, small mesocosms had regular disruptions to species sorting and greater importance of ecological drift and dispersal limitation indicated by lower richness and higher taxa replacement. Together, these results emphasize that environmental fluctuations influence ecosystems over time and its impacts are modified by biotic properties intrinsic to ecosystem size
Frequency-dependent electron power absorption mode transitions in capacitively coupled argon-oxygen plasmas
Phase Resolved Optical Emission Spectroscopy (PROES) measurements combined
with 1d3v Particle-in-Cell/Monte Carlo Collision (PIC/MCC) simulations are
performed to investigate the excitation dynamics in low-pressure capacitively
coupled plasmas (CCPs) in argon-oxygen mixtures. The system used for this study
is a geometrically symmetric CCP reactor operated in a fixed mixture gas
composition, at fixed pressure and voltage amplitude, with a wide range of
driving RF frequencies (2MHzMHz). The measured and
calculated spatio-temporal distributions of the electron impact excitation
rates from the Ar ground state to the Ar state (with a wavelength
of 750.4~nm) show good qualitative agreement. The distributions show
significant frequency dependence, which is generally considered to be
predictive of transitions in the dominant discharge operating mode. Three
frequency ranges can be distinguished, showing distinctly different excitation
characteristics: (i) in the low frequency range (MHz), excitation is
strong at the sheaths and weak in the bulk region; (ii) at intermediate
frequencies (3.5MHzMHz), the excitation rate in the bulk
region is enhanced and shows striation formation; (iii) above 6MHz,
excitation in the bulk gradually decreases with increasing frequency. Boltzmann
term analysis was performed to quantify the frequency dependent contributions
of the Ohmic and ambipolar terms to the electron power absorption.Comment: arXiv admin note: text overlap with arXiv:2205.0644
Multi-messenger observations of a binary neutron star merger
On 2017 August 17 a binary neutron star coalescence candidate (later designated GW170817) with merger time 12:41:04 UTC was observed through gravitational waves by the Advanced LIGO and Advanced Virgo detectors. The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray burst (GRB 170817A) with a time delay of ~1.7 s with respect to the merger time. From the gravitational-wave signal, the source was initially localized to a sky region of 31 deg2 at a luminosity distance of 40+8-8 Mpc and with component masses consistent with neutron stars. The component masses were later measured to be in the range 0.86 to 2.26 Mo. An extensive observing campaign was launched across the electromagnetic spectrum leading to the discovery of a bright optical transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC 4993 (at ~40 Mpc) less than 11 hours after the merger by the One- Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The optical transient was independently detected by multiple teams within an hour. Subsequent observations targeted the object and its environment. Early ultraviolet observations revealed a blue transient that faded within 48 hours. Optical and infrared observations showed a redward evolution over ~10 days. Following early non-detections, X-ray and radio emission were discovered at the transient’s position ~9 and ~16 days, respectively, after the merger. Both the X-ray and radio emission likely arise from a physical process that is distinct from the one that generates the UV/optical/near-infrared emission. No ultra-high-energy gamma-rays and no neutrino candidates consistent with the source were found in follow-up searches. These observations support the hypothesis that GW170817 was produced by the merger of two neutron stars in NGC4993 followed by a short gamma-ray burst (GRB 170817A) and a kilonova/macronova powered by the radioactive decay of r-process nuclei synthesized in the ejecta
Multi-messenger Observations of a Binary Neutron Star Merger
On 2017 August 17 a binary neutron star coalescence candidate (later
designated GW170817) with merger time 12:41:04 UTC was observed through
gravitational waves by the Advanced LIGO and Advanced Virgo detectors.
The Fermi Gamma-ray Burst Monitor independently detected a gamma-ray
burst (GRB 170817A) with a time delay of ∼ 1.7 {{s}} with respect to
the merger time. From the gravitational-wave signal, the source was
initially localized to a sky region of 31 deg2 at a
luminosity distance of {40}-8+8 Mpc and with
component masses consistent with neutron stars. The component masses
were later measured to be in the range 0.86 to 2.26 {M}ȯ
. An extensive observing campaign was launched across the
electromagnetic spectrum leading to the discovery of a bright optical
transient (SSS17a, now with the IAU identification of AT 2017gfo) in NGC
4993 (at ∼ 40 {{Mpc}}) less than 11 hours after the merger by the
One-Meter, Two Hemisphere (1M2H) team using the 1 m Swope Telescope. The
optical transient was independently detected by multiple teams within an
hour. Subsequent observations targeted the object and its environment.
Early ultraviolet observations revealed a blue transient that faded
within 48 hours. Optical and infrared observations showed a redward
evolution over ∼10 days. Following early non-detections, X-ray and
radio emission were discovered at the transient’s position ∼ 9
and ∼ 16 days, respectively, after the merger. Both the X-ray and
radio emission likely arise from a physical process that is distinct
from the one that generates the UV/optical/near-infrared emission. No
ultra-high-energy gamma-rays and no neutrino candidates consistent with
the source were found in follow-up searches. These observations support
the hypothesis that GW170817 was produced by the merger of two neutron
stars in NGC 4993 followed by a short gamma-ray burst (GRB 170817A) and
a kilonova/macronova powered by the radioactive decay of r-process
nuclei synthesized in the ejecta.</p
The legacy of the past : effects of historical processes on microbial metacommunities
Distinguishing the importance of different community assembly mechanisms is an emerging topic in microbial ecology and much focus has been placed in recent years on investigating how contemporary environmental conditions, dispersal and stochastic processes influence the spatial turnover of communities. However, historical events, such as past environmental conditions or dispersal events, can be important as well. We provide a short summary of the processes that can lead to so-called legacy effects, where past biotic or abiotic factors influence the composition of present-day communities. Priority effects, which arise if early colonizers gain advantage over later-arriving species, can lead to persistent legacy effects. In contrast, time-lags in environmental selection can lead to transient legacy effects. Dispersal rates as well as factors that influence the adaptability of species to changing environmental conditions should be important factors that determine the relative importance of contemporary selection versus historical processes and whether legacy effects are likely to be permanent or temporary. Working with microbial communities offers the advantage of feasible time series studies and multi-generation experiments, and can therefore make important contributions to a novel systematic framework on how historical processes shape complex metacommunities in nature